Programmatic Website Screen Shots

I'm checking into the available methods for programmatically taking screenshots of an arbitrary website. For example,

Facebook:

http://clicktoverify.truste.com/pvr.php?page=validate&url=www.facebook.com&sealid=102

Salesforce.com:

http://clicktoverify.truste.com/pvr.php?page=validate&companyName=Salesforce.com,%20Inc.&sealid=102&internal=true

On that page you'll see they have a screensho开发者_StackOverflow中文版t of the referenced site.

What are my options for getting these kinds of screenshots in an automated fashion?

I'm primarily working with PHP, but am open to all suggestions.

Thanks!

Truth of the matter is, the actual process is extremely non-trivial. You can of course manage it but it is a very difficult matter.

That said, there are a ton of webservices that you can use that do exactly this. One such example is http://www.thumbalizr.com/ although they are by no means alone in this.